If the circumference of a circle of radius ‘r’ and the perimeter of a square of side ‘a’ are equal,

If the circumference of a circle of radius ‘r’ and the perimeter of a square of side ‘a’ are equal, then the ratio of areas of the circle to that of square is (a) 4 : π (b) π : 4 (c) π² : 16 (d) π² : 4